2003 International Mechanical Pulping Conference 341

PRACTICAL EXPERIENCE WITH ENZYMATIC PITCH

CONTROL IN MECHANICAL PULPING PROCESSES

Xiang H. WangChengliang JiangEnzymatic Deinking Technologies (EDT), LLCNorcross, GA 30093 USA

AbstractOver the past few years, extensive work has been conducted by EDT to implement a novel enzymatic technology aimed at solving the wood extractive (pitch) induced problems through addressing the root-cause issues. New application technologies and approaches have been developed to facilitate the risk-managed implementation of the enzymatic pitch control technology in different mills. Vital to successful implementation is an innovative pitch measurement technology which measures Apparent Pitch Content™, the APC™ Test. This patent-pending method was developed to measure the amount of pitch that is responsible for causing pitch-related problems.

Since its first successful application at Nanping Paper Mill in China in early 2000, EDT’s EnzOx™ enzymatic pitch treatment has been running in mills across North America and Europe. While initially thought of as only a solution for deposit control, pitch control now is known to incorporate a variety of solutions to problems caused by extractives. Paper machine efficiency is improved by effective cleaning of the equipment, including cleaner felts and reduced deposits. Product quality, such as strength, printability, and printing press runnability, is improved by removal of pitch that hinders inter-fiber bonding. Production costs are lowered resulting from reduction or elimination of kraft for strength, clay for friction, cleaning chemicals for smoother operations, and bleaching chemicals for brightness losses due to wood aging.

IntroductionMechanical pulping processes offer several advantages when compared with fully bleached kraft pulp or other chemical pulps. For example, mechanical pulping processes provide much higher pulp yield (up to 90%) and use fewer chemicals and less water [1]. Apart from a small percentage of water-soluble materials which is removed during the pulping, mechanical pulp contains all constituents of the parent wood, including resin. Furthermore, in mechanical pulping, the fiber structure is compressed repeatedly and finally disrupted, promoting movement of the resinous materials. As a result, wood extractives are released from wood and fibers during the production and further treatment of mechanical pulp. Subsequently, the resin may redeposit back onto the surface of the fibers. When resins are retained on the fiber surfaces, the paper properties will be affected.

The resin may also form aggregates with other dissolved and colloidal substances and process chemicals, causing deposits and creating runnability and final product quality problems.

Considerable research has been conducted on development of paper strength, and there is a large amount of literature on the subject demonstrating the contribution of many factors. A factor which has received scant attention is the effect on paper strength of resinous materials deposited on the fiber surface. Most previous work on paper strength has been done on chemical pulps in which the residual resin content on the fiber surface is quite small. A number of recent studies [2-12] demonstrated that the paper strength is increased significantly when mechanical pulp is chemically treated to remove the resinous materials from the fiber surfaces. For example, Brandal and Lindheim [2] demonstrated that the presence of resins in the paper sheet, particularly those resins having long hydrocarbon chains, had detrimental effects that resulted in reduced strength. Extraction treatment of the groundwood pulp made from Scotch pine and Norway spruce with organic solvents substantially increased the strength of the pulp. For example, the tear index was increased by 35%, and burst index by as much as 80%, after acetone extraction treatment. Similar results were recently reported by Korpela [3] for ethanol extraction of PGW pine pulp. He further showed that the dissolution of resinous extractives could be effectively achieved by hydrogen peroxide bleaching at high alkalinity, thereby eliminating the detrimental effects of resin on pulp strength.

Rundlof et al. [4] studied the correlation of the decrease of paper strength with the amount of lipophilic extractives present on the fiber surfaces. Using sophisticated surface analytical techniques (e.g., ESCA), they quantified the chemical compositions on the fiber surfaces. It was shown that the paper strength decrease started to occur at about 50% of monolayer coverage of the fiber surfaces by extractives. Furthermore, it was shown that the effect of extractives, present in both colloidal and dissolved forms, was as detrimental for kraft pulp as for mechanical pulp and that adsorption of extractives on fine fibers was higher than that on coarse fibers [5].

Due to their hydrophobic surface properties, resins are good lubricants and thus reduce the coefficient of friction (COF) of the paper sheet, causing various problems at the reel and in printing operations [13].

Traditional approaches for controlling pitch problems rely on the use of a variety of chemicals such as talc, cationic fixatives, dispersants, and detackifiers. While partially effective, however, none of them provides a cost-effective solution to the full breadth of pitch-related problems.

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This paper presents a novel enzymatic technology that has proven to provide a cost-effective solution for addressing the many facets of these resin-related problems. The fundamental aspects of the technology and the APC™ Test, an innovative pitch quantification method targeted solely at the problematic pitch, are discussed. Mill application results are summarized based on a variety of physical properties to demonstrate the effectiveness of the enzymatic pitch control technology.Fundamentals of the Enzymatic Technology

Several terms, including wood extractives, pitch, wood resin, and neutral extractives have been used interchangeably by the pulp and paper industry to refer to the lipophilic, resinous materials present in the pulping and papermaking processes. According to Back and Allen [13], the major lipophilic materials in wood are composed of four classes of components: fatty acids, their metal soaps and glyceride esters; resin acids and terpenoids; sterols and fatty acid esters; and fatty alcohols and waxes. The compositions and amount of each component in the papermaking process vary greatly, depending on many factors including tree species, location, season, age of the trees, temperature, pulping process, and chemicals used. Not all of the wood extractives are detrimental or have the same detrimental effects. Wood extractives also differ by tree species, age of the tree at harvesting, chip age, and the season of the year. It has been shown that the long chain fatty esters and glycerides are particularly detrimental to the paper quality and paper machine runnability, and that traditional pitch control treatments are not fully effective for solving the relevant problems [14-18].

The mechanism underlying the enzymatic technology for the control of wood extractive problems is the use of lipolytic enzymes to break down glycerides into glycerol and fatty acids, as shown in the following reaction:

The fatty acids created by the enzymatic hydrolysis can be readily managed by fixation onto the fibers with cationic coagulants and retention aids, as with rosin sizing.

Based on unique technical expertise in enzymology and extensive research on enzyme performance across different tree species and under multiple process conditions, EDT has developed this innovative enzyme technology. EDT’s

EnzOx™ technology is characterized by a mill-specific approach to product and applications development.

Treatments are tailored with optimal blends of enzymes to address each mill’s tree species and mill operating conditions. Application methods are tailored to each mill’s equipment, configuration, water loops, and process conditions. Lastly, EDT utilizes its innovative pitch quantification method, the APC™ Test, that enables the mill to monitor and optimize the performance of the enzyme treatment over time.

Innovative Pitch Quantification Method – The APC™ TestAs mentioned above, not all the pitch components are detrimental to papermaking. For example, not all forms of triglycerides present in the system cause deleterious effects.

It has been shown that wood resins in the pulp stock are present in three states: “free” resins in the solution that are in dissolved and colloidal forms; surface resins that are adsorbed or attached on the fiber surface; and encapsulated resins that are inside the fiber. The resins encapsulated in the fiber do not contribute to the problems commonly encountered with pitch. Only the free and surface resins create problems for paper machine operation and product quality. All existing extractive analysis methods are based on the solvent extraction of the entire pulp stock. Such analytical data provide poor, or even no, correlation with actual problems encountered at mills. Mills have desired for many years to have a quick testing technique that can help monitor the problematic wood resin content in the pulping and papermaking processes.

EDT’s patent-pending APC™ Test was developed with this objective in mind. The test quantifies the amount of triglycerides (TG) in the pulp stock that are present in both “free” and surface-bound forms. It therefore provides a direct measurement of the trouble-inducing glycerides. The APC™ Test has proven to be a highly reliable, accurate, and quick technique to evaluate operating strategies and optimize the enzymatic pitch control technology. The test is readily deployable at mill conditions (i.e., without use of any hazardous chemicals) and provides results within one hour. EDT uses the test at mill sites to tailor the EnzOx™ application and monitor the performance of the enzyme program. Over the past two seasons of daily testing over various geographies, the APC™ Test data has been proven to correlate to machine runnability and product quality parameters. Mills have also found this tool to be helpful in managing their wood procurement and processing practices.

Enzymatic Development of Paper Strength The ability of wood fibers to form bonds with each other is a fundamental property of the fibers and a necessary requirement for paper strength. Since the strength of

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2003 International Mechanical Pulping Conference 343

individual fibers is higher than the strength of bonds formed between fibers, the paper sheet strength development is driven by the fiber-to-fiber bonding strength regulated primarily by hydrogen bonding. However, in the presence of wood resins the surfaces of fibers, particularly fine fibers, are contaminated by these unwanted substances, as shown schematically in Figure 1. As a result, the inter-fiber bonding is blocked, thereby reducing the number of hydrogen bonding sites and sheet consolidation. This leads to a reduction in paper strength and friction, as illustrated in Figure 2.

In the presence of lipolytic enzymes, the triglycerides are hydrolyzed into glycerol and fatty acids. These catalysts have an interfacial preference to bulk solutions, and hence the surface bound TGs will be first attacked, producing cleaner fiber surfaces [16]. As a result, the number of

Figure 1. Schematic presentation of paper sheet formation by various fractions of fibers and the distribution of resinous materials on the fiber surfaces.

Figure 2. Schematic presentation of interaction of surface-bound and colloidal resins on fiber surface and subsequent spreading during paper sheet formation and drying.

hydrogen bonding between fibers increases, leading to greater paper strength. This is clearly demonstrated in Figure 3. As the triglycerides on the fiber surface are modified by the enzymes, the content of TG retained in the

paper sheet decreases, and the sheet tensile strength increases considerably.

It has been shown that even a small amount of wood extractives (i.e., less than a monolayer of resin) can have a detrimental impact on the strength and other properties of the sheet. In Northern mechanical pulping mills whose furnish is composed of spruce and a minor percentage of pine, wood extractives, even though present in less quantity when compared to southern mills, have had significant detrimental impacts on the paper strength. It is therefore likely that the enzymatic pitch treatment technology is applicable for a wide variety of tree species worldwide.

Figure 3. Tensile strength as a function of content of surface TG retained in the handsheet for groundwood pulp from a northeastern mill. The pulp was treated at various dosages of a particular EnzOx™ blend of enzymes to remove the TG.

Development of Application TechnologyThough the basic mechanism of this technology has been understood for years, its use in mills has not progressed far due to the complexity of applying this technology at mill scale. Progress has been further impeded by several well-known failed attempts by both paper companies and suppliers to the industry balanced against the few successes that took place at unique facilities.

Proper application has proven to be crucial for the success of the enzyme technology at mills. Due to the differences in mill tree species, processes, and operating conditions, different application technologies are required for each individual mill. EDT conducts a comprehensive analysis of a mill’s situation to determine the optimal application conditions prior to each mill’s application startup. For example, with the help of the APC™ Test, a complete profile of the triglycerides (TG) is determined to depict the flow and distribution of the resinous materials throughout the mill, as exemplified in Figure 4 for a southern TMP newsprint mill. It has been established at this mill that without the EnzOx™ treatment, there is a significant buildup of resinous materials at the paper machine.

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Furthermore, due to the high specific surface areas, fine fibers contain substantially higher surface TG.

Figure 4. Profile of TG content in the pulping and paper-making processes of a southern TMP newsprint mill.

To serve varying mill conditions with high cost-efficacy, EDT develops enzyme formulations that are specifically tailored to the individual mill for the effects of tree species, woodyard management, process conditions such as temperature and pH, and certain other factors. It has been found that the tree species has a significant influence on the performance of a particular blend of enzymes.

Other important factors in developing an effective application strategy include location of enzyme addition and incorporation with other mill chemistries. Also critical is the management of by-products from the TG conversion.

Mill ResultsSince EDT’s first successful implementation at Nanping Paper Mill in China in early 2000, the EnzOx™ enzymatic technology has been applied in mills across North America and Europe. The combination of mill-specific EnzOx™ product and application technology has enabled the mills to cost-effectively solve a variety of problems related to wood extractives. A description of some of the benefits achieved at the mills follows:

Improved paper product quality.With the help of the EnzOx™ enzymatic treatment, mills have been able to produce paper products of significantly improved strength and coefficient of friction (COF). Depending on the processes, enzyme blends, and dosages, an average of 5-15% increase in paper strength and 10-35% increase in COF have been obtained. This is shown in Figure 5 for a TMP newsprint mill in the US. The improved fiber bonding also produces paper of lower porosity, lower bulk, and higher sheet uniformity, reducing linting and

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Figure 5. Paper strength (tensile and tear), coefficient of friction (COF) and porosity as a function of the headbox TG content for a TMP newsprint in the U.S.

2003 International Mechanical Pulping Conference 345

dusting problems. It has been shown that the coating performance and printability of the paper treated with EnzOx™ enzymes are considerably improved.

Improved paper machine efficiency.

The enzyme treatment has been shown to be highly effective in cleaning the pulping and papermaking process equipment, reducing deposition and felt filling. Reduced deposits and a stronger sheet have also contributed to fewer breaks. As a result, the mills can run the paper machines faster with less down time, and achieve higher paper machine production efficiencies.

Reduced production costs.

Continuous application of the enzyme product keeps the mill process free of contamination by the wood extractives. The process equipment and paper machines, particularly felts, are cleaner. This leads to a significant reduction in chemicals used for washing and cleaning. Increased paper strength enables mills to reduce or eliminate kraft pulp usage, in most cases by as much as 5-10% kraft in the fiber furnish. Simultaneously, improved COF allows the mills to reduce or eliminate the usage of clays. Some mills previously aged the woodchips to reduce the amount of wood extractives. The enzyme treatment enables mills to use fresh chips, reducing the bleach chemical costs. Wood aged to reduce extractives can lower brightness as much as 5% ISO. Better wood management greatly facilitates wood operations and even maximizes cash flow.

ConclusionsThe EnzOx™ enzymatic pitch control technology is a powerful tool that can enable mills to improve quality, increase machine efficiency, and reduce overall costs. This is especially valuable in the difficult market in which many of these mechanical pulping mills operate. While highly effective, it is a rather complex technology, both to formulate a product, apply the program, and optimize operations to maximize the value. For this reason, EDT's mill-specific approach in tailoring the product blend and customizing its application is essential. Equally important is the need to factor in the ramifications of the enzymatic pitch control treatment to other chemistries and colloidal materials in the mill.

The effectiveness of EDT's program not only enables mills to run better under their current operational strategies, but presents new opportunities to run the mill differently. Issues such as reduced kraft purchases, different tree species procurement, and modified wood yard management are common areas for savings. Key to the development of the EnzOx™ product and its optimal application in each mill is the APC™ Test. This quick and effective tool provides accurate measurement of the problematic components

throughout the mill system. Ongoing use of the APC™ Testenables mills to monitor efficacy of the system, deal with issues such as seasonality, and continue optimization to gain the greatest value from the technology.

ReferencesKAPPEL, J., “Mechanical Pulps: From Wood to Bleached Pulp”, TAPPI Press, 396 (1999).BRANDAL, J., AND LINDHEIM, A., “The Influence of Ex-tractives in Groundwood Pulp on Fibre Bonding”, Pulp Pa-per Magazine Canada, T-432-T-435, October (1966).KORPELA, A., “Improving the Strength of PGW Pine Pulp by Alkaline Peroxide Treatment”, Nordic Pulp Paper Res. J. 17(2): 183-186 (2002).RUNDLÖF, M., SJÖLUND, A-K., STRÖM, H., AND ASELL, I., “The Effect of Dissolved and Colloidal Substanc-es Released from TMP on the Properties of TMP Fines”, Nordic Pulp Paper Res. J. 15(4): 256-265 (2000).SUNDBERG, A., HOLMBOM, B., WILLFÖR, S., PRANOVICH, A., “Weakening of Paper Strength by Wood Resin”, Nordic Pulp Paper Res. J. 15(1): 46-53 (2000).FRANCIS, D.W., AND OUCHI, M.D., “Effect of Dissolved and Colloidal Solids on Newsprint Properties”, J. Pulp Paper Sci. 27(9): 289-295 (2001).LANOUETTER, R., BERGERON, F., AND DANEAULT, C., “Characterization of Jack Pine –Spruce Mixtures”, in TAPPI Pulping Conf. Proc. (2001). OTERO, D., SUNDBERG, K., BLANCO, A., NEGRO, C., AND TIJERO, J., “Effects of Wood Polysaccharides on Pitch Deposition”, Nordic Pulp Paper Res. J. 15(5): 607-613 (2000).ALLISION, R.W., “Effects of Peroxide Bleaching on the Physical Properties of Pressurized Groundwood from Pinus Radiata”, in 1983 International Mechanical Pulping Proceed-ings, 59-65.MOLDENIUS, S., “The Effects of Peroxide Bleaching on the Strength and Surface Properties of Mechanical Pulping”, J. Pulp Paper Sci. J172-177, November (1984).PENG, G., AND ROBERTS, J.C., “Resin Acid Formation during Thermomechanical Pulping”, in 1996 International Enviornmental Conference & Exhibits, 1-12.LANOUETGTER, R., VALADE, J.L., AND LAW, K-N., “Influence of Chip Pre-Treatment on the Reduction of Ex-tractives Content in High Yield Pulping of Jack Pine”, in 2001 Pulping Conf. Proc. BACK, E.L., AND ALLEN, L.H., Pitch Control, Wood Res-in and Deresination, TAPPI Press, Atlanta (2000).FISHER, K., AND MESSNER, K., “Reducing Troublesome Pitch in Pulp Mills by Lipolytic Enzymes” TAPPI J. 75(2): 130-134 (1992).FISCHER, K., PUCHINGER, L., SCHLOFFER, KREINER, W., AND MESSNER, K., “Enzymatic Pitch Control of Sulfite Pulp on Pilot Scale” J. Biotechnol. 27: 341-348 (1993).FISHER, K., AND MESSNER, K., “Adsorption of Lipase on Pulp Fibers During Biological Pitch Control in Paper Indus-try”, Enzyme Microb. Technol. 14(6): 470-473 (1992).STACK, K.R., STEVENS, E.A., RICHARDSON, D.E., PARSONS, T., AND JENKINS, S., “Factors Affecting the Deposition of Pitch in Process Waters and Model Disper-sions”, in Appita Annual Gen. Conf. Proc. Vol.1, 59-66 (1998).SMITH, W., “Survey of Pitch Control in Newsprint Mills Using Pine”, in 1995 Papermakers Conference Proceedings, 345-350.